12/02/09 Estimate with Decimals #2

1. 12/02/09 Estimate with Decimals #2 LT: I will estimate to solve decimal problems. Warm Up: You do not need a new lesson heading. Write each fraction or decimal as a percent. (You may use your fraction, decimal, percent wheel.) A) B) C) D) 0.25 E) 0.6 F) 0.01 G) 0.1 H) 1.0 1 2 1 3 3 4 Today’s Plan: -Warm-up -Lesson -Assignment Learning Target: -I will estimate to solve decimal problems.

2. 4-1 Estimate with Decimals 6.7 +4.9 +5 Course 2 Insert Lesson Title Here Try This: Example 1A Estimate by rounding to the nearest integer. A. 6.7 + 4.9 7 7 ≥ 5, so round to 7. 9 > 5, so round to 5. Estimate 12

3. 4-1 Estimate with Decimals 19.2 –13.6 –14 Course 2 Insert Lesson Title Here Try This: Example 1B Estimate by rounding to the nearest integer. B. 19.2 – 13.6 19 2 < 5, so round to 19. 6 > 5, so round to –14. Estimate 5

4. 4-1 Estimate with Decimals 61.3 + (–19) + (–18.84) Course 2 Insert Lesson Title Here Try This: Example 1C Estimate by rounding to the nearest integer. C. 61.3 + (–18.84) 61 3 < 5, so round to 61. 8 > 5, so round to –19. 42 Estimate

5. 4-1 Estimate with Decimals Course 2 You can use compatible numbers when estimating for multiplication and division. Compatiblenumbers are numbers that replace the numbers in the problem and are easier to use.

6. 4-1 Insert Lesson Title Here Course 2

7. 4-1 Estimate with Decimals 45.99  2.31  2 Course 2 Insert Lesson Title Here Additional Example 2A: Estimating with Decimals Use compatible numbers to estimate. A. 45.99 · 2.31 Round to the nearest multiple of 10. 50 3 < 5, so round to 2. 100 Estimate

8. 4-1 Estimate with Decimals Course 2 Insert Lesson Title Here Additional Example 2B: Estimating with Decimals Use compatible numbers to estimate. B. 51.33 ÷ (–7.98) 51 is prime, so round to 49. 51.33 49 –7.98 –7 divides into 49 without a remainder. –7 49 ÷ –7 = –7 Estimate

9. 4-1 Estimate with Decimals 39.62  4.99  5 Course 2 Insert Lesson Title Here Try This: Example 2A Use compatible numbers to estimate. A. 39.62 · 4.99 Round to the nearest multiple of 10. 40 9 > 5, so round to 5. 200 Estimate

10. 4-1 Estimate with Decimals Course 2 Insert Lesson Title Here Try This: Example 2B Use compatible numbers to estimate. B. 19.42 ÷ (–4.88) 19 is prime, so round to 20. 19.42 20 –4.88 –5 divides into 20 without a remainder. –5 20 ÷ –5 = –4 Estimate

11. 4-1 Estimate with Decimals Course 2 Insert Lesson Title Here Additional Example 3: Application Cara spent $58.80 on 4.8 pounds of lobster and calculated that she spent about $12 per pound of lobster. Use estimation to check whether her calculation is reasonable. $60 $58.80 Round to the nearest multiple of 10. 8 > 5, so round to 5. 5 4.85 60 ÷ 5 = 12 Estimate The estimate is the same as Cara’s calculation. The lobster cost about $12 per pound.

12. 4-1 Estimate with Decimals Course 2 Insert Lesson Title Here Try This: Example 3 Clem spent $18.43 on 11.7 pounds of apples. Is it reasonable to say that Clem spent about $2 per pound on apples? Round to the nearest multiple of 10. $20 18.43 10 divides evenly into 20 without a remainder. 10 11.7 20 ÷ 10 = 2 Estimate The estimate is the same as Clem’s calculation. The apples cost about $2 per pound.

13. 12/02/09 Estimate with Decimals #2 LT: I will estimate to solve decimal problems. Assignment Pg 194 #1-20 Today’s Plan: -Warm-up -Lesson -Assignment Learning Target: -I will estimate to solve decimal problems.